1. Field of the Invention
The present invention relates generally to improved methods for growing silicon dioxide layers on substrates, such as in semiconductor manufacture, using atomic layer deposition processes. The methods of this invention facilitate exercising extremely precise control over the properties of a silicon dioxide layer applied, for example, to a gate oxide or a dielectric layer. The methods of this invention have particular utility in fabricating gate spacers, gate oxides, silicide blocking layers, bit line spacers, inter-level dielectric layers, etch stoppers, and related final or intermediate products in semiconductor fabrication.
2. Description of the Related Art
In manufacturing a semiconductor device, a silicon dioxide layer is typically formed on a substrate surface by such conventional techniques as chemical vapor deposition (CVD), low-pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD). These techniques are recognized as providing a good step coverage at a comparatively low temperature. As the density of a semiconductor device increases, however, so too do the heights of the respective elements which comprise the device. As a result, a problem arises due to increased pattern density variation and a corresponding decrease in uniformity.
As taught in U.S. Pat. No. 6,090,442 (Klaus '442), which patent is incorporated herein by reference, one approach to these recognized problems was to use an atomic layer deposition (ALD) technique. Klaus '442 teaches, however, that the big drawback to ALD techniques was that they typically required temperatures greater than 600° K. and reactant exposures of greater than 109 L (where 1 L=10−6 Torr see) for the surface reactions to reach completion. Such high temperature and high exposure procedures are not desirable for ultra-thin film deposition applications for various reasons including the difficulty of carrying out such procedures.
An improved approach to such problems was taught by the Klaus '442 patent. Klaus '442 provides a method for growing atomic layer thin films on functionalized substrates at room temperatures utilizing catalyzed binary reaction sequence chemistry. More particularly, according to the Klaus '442 patent, a two-step atomic layer deposition (ALD) process, using two catalyst-assisted “half-reactions” carried out at room temperature, can be used to grow a silicon dioxide film on an OH terminated substrate.
In a specific embodiment, Klaus '442 utilizes SiCl4 as a “first molecular precursor” and pyridine as a catalyst. First, the substrate is functionalized with OH− as a “first functional group,” for example using H2O. Next, the functionalized substrate is exposed to a catalyst that is a Lewis base or Lewis acid (e.g., pyridine) and a first molecular precursor which includes the primary element of the film to be grown as well as a second functional group (e.g., SiCl4). As described by Klaus '442, in the first “half-reaction,” the catalyst interacts with the first functional group of the functionalized substrate; then, the first molecular precursor reacts with the first functional group (which has been activated by the catalyst) resulting in a displacement of the catalyst and a bond between the first functional group of the substrate and the primary element of the first molecular precursor. Taken together, these two reactions comprise the first “half-reaction” and represent the beginning of film formation with the second functional group now located across the surface of the film.
At this point in the Klaus '442 process, excess first molecular precursor and any byproducts are purged from the reaction chamber, and the partially-reacted substrate is exposed to additional catalyst and a second molecular precursor. The catalyst activates the exposed second functional group along the surface of the film by reacting with it and with a second molecular precursor, resulting in a displacement of the second functional group and also resulting in a bond to the primary element of the first molecular precursor. Now, the second molecular precursor reacts with the bond between the primary element of the first molecular precursor and the catalyst resulting in a displacement of the catalyst and the deposition of the first functional group on the newly-grown surface layer, thereby completing a full growth/deposition cycle and restoring the substrate surface to a functionalized state in preparation for the next cycle.
Although the catalyst-assisted deposition processes of the Klaus '442 patent represent substantial advances in ALD technology, and do make possible room-temperature ALD, it has been found that the surface density, uniformity and quality of thin films grown using the Klaus '442 technique will not meet increasingly demanding standards in the semiconductor industry. With the seemingly never-ending evolution toward ever-smaller microelectronic components, ever-more precise control is required over the properties of semiconductor devices. Such precision control requires increasingly highly uniform surface properties and pattern density. It has now been found that novel improvements in ALD techniques in accordance with this invention produce thin films for semiconductor devices having superior surface density and significantly more uniform surface properties than could be achieved with prior art methods resulting in surprisingly more precise control over the properties of a thin film layer and in higher quality semiconductor devices suitable for modern miniaturization applications.
The Klaus '442 patent represents that: “Strong amine bases like triethylamine ((C2H5)3N) have been shown to form salt compounds like triethylammonium chloride (NH+(C2H5)3Cl−) in the presence of chlorosilanes. These salts could poison the surface and degrade the reaction efficiency as they build up.” (column 9, line 24˜28). Thus, Klaus '442 appears to teach away from the presence of triethylamine, i.e. tertiary aliphatic amine, in ALD applications. But, in this invention, control of process conditions coupled with a variety of purge methods have been found to solve the above problems.